Conventional ozone bleaching of cellulosic pulps in an aqueous medium produces significant degradation of the pulp. A variety of different protectors have been suggested to be added to the slurry to protect the cellulose from ozone attack. However, most have either been ineffective in protecting or were required in very substantial amounts.
The use of alcohol such as methyl-alcohol in the aqueous medium surrounding the pulp fibers during the ozone bleaching stage was suggested a number of years ago but was not found to be particularly effective until recently when applied in a particular manner to obtain significant improvement in pulp viscosity (strength) after the ozone stage relative to what could be obtained using conventional ozone bleaching (see U.S. patent application Ser. No. 08/056,496 filed by Solinas et al. on May 3, 1993).
It is also known to operate the ozone bleaching stage at a temperature below room temperature as described in the Kobayashi reference and as further discussed in U.S. patent application Ser. No. 08/024,056 filed Mar 1, 1993 by van Heiningen et al, now abandoned.